Traditional simulation methods are unable to meet the requirements of lunar takeo simulations, such as high force output precision, low cost, and repeated use. Considering that cable-driven parallel mechanisms have th...Traditional simulation methods are unable to meet the requirements of lunar takeo simulations, such as high force output precision, low cost, and repeated use. Considering that cable-driven parallel mechanisms have the advantages of high payload to weight ratio, potentially large workspace, and high-speed motion, these mechanisms have the potential to be used for lunar takeo simulations. Thus, this paper presents a parallel mechanism driven by nine cables. The purpose of this study is to optimize the dimensions of the cable-driven parallel mechanism to meet dynamic workspace requirements under cable tension constraints. The dynamic workspace requirements are derived from the kinematical function requests of the lunar takeo simulation equipment. Experimental design and response surface methods are adopted for building the surrogate mathematical model linking the optimal variables and the optimization indices. A set of dimensional parameters are determined by analyzing the surrogate mathematical model. The volume of the dynamic workspace increased by 46% after optimization. Besides, a force control method is proposed for calculating output vector and sinusoidal forces. A force control loop is introduced into the traditional position control loop to adjust the cable force precisely, while controlling the cable length. The e ectiveness of the proposed control method is verified through experiments. A 5% vector output accuracy and 12 Hz undulation force output can be realized. This paper proposes a cable-driven parallel mechanism which can be used for lunar takeo simulation.展开更多
We first analyzed the force and motion of naval aircraft during launching process.Further,we investigated the ship deck with the form of a ramp and established deck motion model and ship airwake model.Finally,we condu...We first analyzed the force and motion of naval aircraft during launching process.Further,we investigated the ship deck with the form of a ramp and established deck motion model and ship airwake model.Finally,we conducted simulations at medium sea.Results showed that the effects of deck motion on takeoff varied with initial phases,and airwake could help reducing aircraft′s sinkage.We also found that the deck motion played a major role in the effects caused by the interaction of deck motion and ship airwake.展开更多
Battery powered vertical takeoff and landing(VTOL) aircraft attracts more and more interests from public, while limited hover endurance hinders many prospective applications. Based on the weight models of battery, mot...Battery powered vertical takeoff and landing(VTOL) aircraft attracts more and more interests from public, while limited hover endurance hinders many prospective applications. Based on the weight models of battery, motor and electronic speed controller, the power consumption model of propeller and the constant power discharge model of battery, an efficient method to estimate the hover endurance of battery powered VTOL aircraft was presented. In order to understand the mechanism of performance improvement, the impacts of propulsion system parameters on hover endurance were analyzed by simulations, including the motor power density, the battery capacity, specific energy and Peukert coefficient. Ground experiment platform was established and validation experiments were carried out, the results of which showed a well agreement with the simulations. The estimation method and the analysis results could be used for optimization design and hover performance evaluation of battery powered VTOL aircraft.展开更多
A nonlinear and time-varying gyroplane jump takeoff dynamics model considering the unsteady ground effect and the rapid blade-pitch increase(RBPI) is developed and validated against the experiment data.The precisions ...A nonlinear and time-varying gyroplane jump takeoff dynamics model considering the unsteady ground effect and the rapid blade-pitch increase(RBPI) is developed and validated against the experiment data.The precisions of the proposed model,an experienced Hollmann model and three other simplified models are compared by displaying the height and rpm time histories of those models and the experimental data.The mean square errors(MSE) of the height histories and maximum height errors(MHE) between those models are calculated and given out.The statistics provide a kind of evaluation method of importance of the unsteady ground effect,RBPI,and the induced velocity on jump takeoff performance in vertical phase.The impact of the unsteady ground effect and RBPI on the thrust and induced velocity of the experimental rotor of a small scale platform is analyzed.The study indicates that the proposed model agrees better with the experimental data than other models.It is useful for predicting the gyroplane jump takeoff performance for design.展开更多
The formal modeling and verification of aircraft takeoff is a challenge because it is a complex safety-critical operation.The task of aircraft takeoff is distributed amongst various computer-based controllers,however,...The formal modeling and verification of aircraft takeoff is a challenge because it is a complex safety-critical operation.The task of aircraft takeoff is distributed amongst various computer-based controllers,however,with the growing malicious threats a secure communication between aircraft and controllers becomes highly important.This research serves as a starting point for integration of BB84 quantum protocol with petri nets for secure modeling and verification of takeoff procedure.The integrated model combines the BB84 quantum cryptographic protocol with powerful verification tool support offered by petri nets.To model certain important properties of BB84,a new variant of petri nets coined as Quantum Nets are proposed by defining their mathematical foundations and overall system dynamics,furthermore,some important system properties are also abstractly defined.The proposed QuantumNets are then applied for modeling of aircraft takeoff process by defining three quantum nets:namely aircraft,runway controller and gate controller.For authentication between quantum nets,the use of external places and transitions is demonstrated to describe the encryptiondecryption process of qubits stream.Finally,the developed takeoff quantum network is verified through simulation offered by colored petri-net(CPN)Tools.Moreover,reachability tree(RT)analysis is also performed to have greater confidence in feasibility and correctness of the proposed aircraft takeoff model through the Quantum Nets.展开更多
The bio-inspired aerial–aquatic vehicle off ers attractive perspectives for future intelligent robotic systems.Cormorant’s webbed-feet support water-surface takeoff is a typical locomotion pattern of amphibious wate...The bio-inspired aerial–aquatic vehicle off ers attractive perspectives for future intelligent robotic systems.Cormorant’s webbed-feet support water-surface takeoff is a typical locomotion pattern of amphibious water birds,but its highly maneuverable and agile kinetic behaviors are inconvenient to measure directly and challenging to calculate convergently.This paper presents a numerical Computational Fluid Dynamic(CFD)technique to simulate and reproduce the cormorant's surface takeoff process by modeling the three-dimensional biomimetic cormorant.Quantitative numerical analysis of the fluid flows and hydrodynamic forces around a cormorant’s webbed feet,body,and wings are conducted,which are consistent with experimental results and theoretical verification.The results show that the webbed feet indeed produced a large majority of the takeoff power during the initial takeoff stage.Prior lift and greater angle of attack are generated to bring the body off the water as soon as possible.With the discussion of the mechanism of the cormorant’s water-surface takeoff and the relevant characteristics of biology,the impetus and attitude adjustment strategies of the aerial–aquatic vehicle in the takeoff process are illustrated.展开更多
Since the construction industry has been adopting Building Information Modeling(BIM)as the standard practice for design,engineering,and fabrication in the recent decade,many Construction Management(CM)programs at U.S....Since the construction industry has been adopting Building Information Modeling(BIM)as the standard practice for design,engineering,and fabrication in the recent decade,many Construction Management(CM)programs at U.S.universities have started to introduce BIM for cost estimating in their curriculum.Although considered as the fifth dimension beyond 3D and schedule,BIM for cost estimating in many cases is still used merely as an alternative model-based quantity takeoff method to the traditional plan-based approach.The disconnection between automated quantity takeoff and cost estimating,however,still exists,and the benefits of the BIM process in a project life cycle can not be fully understood by CM students without realizing its impact in the preconstruction phase.To bridge these gaps in a CM curriculum,an Advanced Cost Estimating course for CM programs has been developed that focuses on integrating BIM in both the takeoff and estimating process.The new course streamlines the connection between model-based quantity takeoff and cost estimating with the help of a combination of multiple construction software programs.Through the integration between the software,quantity data from a BIM model can be seamlessly transferred to a construction cost database for bid pricing and reporting.This paper presents the development of the new Advanced Cost Estimating course as a case study,including its objectives,layout,and assessment methods,and provides empirical and valuable insights on how to integrate BIM in a cost estimating course for a CM curriculum.展开更多
In the paper, we present a detailed analysis of the takeoff mechanics of fruitflies which perform voluntary takeoff flights. Wing and body kinematics of the insects during takeoff were measured using high-speed video ...In the paper, we present a detailed analysis of the takeoff mechanics of fruitflies which perform voluntary takeoff flights. Wing and body kinematics of the insects during takeoff were measured using high-speed video techniques.Based on the measured data, inertia force acting on the insect was computed and aerodynamic force and moment of the wings were calculated by the method of computational fluid dynamics. Subtracting the aerodynamic force and the weight from the inertia force gave the leg force. The following has been shown. In its voluntary takeoff, a fruitfly jumps during the first wingbeat and becomes airborne at the end of the first wingbeat. When it is in the air, the fly has a relatively large "initial" pitch-up rotational velocity(more than5 000°/s) resulting from the jumping, but in about 5 wingbeats, the pitch-up rotation is stopped and the fly goes into a quasi-hovering flight. The fly mainly uses the force of jumping legs to lift itself into the air(the force from the flapping wings during the jumping is only about 5%–10% of the leg force). The main role played by the flapping wings in the takeoff is to produce a pitch-down moment to nullify the large "initial" pitch-up rotational velocity(otherwise, the fly would have kept pitching-up and quickly fallen down).展开更多
Owing to the strong coupling among the hydrodynamic forces,aerodynamic forces and motion of amphibious aircraft during the water takeoff process,the water takeoff performance is difficult to calculate accurately and q...Owing to the strong coupling among the hydrodynamic forces,aerodynamic forces and motion of amphibious aircraft during the water takeoff process,the water takeoff performance is difficult to calculate accurately and quickly.Based on an analysis of the dynamics and kinematics characteristics of amphibious aircraft and the hydrodynamic theory of high-speed planing hulls,a suitable mathematical model is established for calculating the hydrodynamics of aircraft during water takeoff.A pilot model is designed to illustrate how pilots are affected by the lack of visual reference and the necessity to simultaneously control the pitch angle,flight velocity and other parameters during water takeoff.Combined with the aerodynamic model,engine thrust model and aircraft motion model,a digital virtual flight simulation model is developed for amphibious aircraft during water takeoff,and a calculation method for the water takeoff performance of amphibious aircraft is proposed based on digital virtual flight.Typical performance indicators,such as the liftoff time and liftoff distance,can be obtained via digital virtual flight calculations.A comparison of the measured flight test data and the calculation results shows that the calculation error is less than 10%,which verifies the correctness and accuracy of the proposed method.This method can be used for the preliminary evaluation of airworthiness compliance of amphibious aircraft design schemes,and the relevant calculation results can also provide a theoretical reference for the formulation of flight test plans for airworthiness certification.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51405024)
文摘Traditional simulation methods are unable to meet the requirements of lunar takeo simulations, such as high force output precision, low cost, and repeated use. Considering that cable-driven parallel mechanisms have the advantages of high payload to weight ratio, potentially large workspace, and high-speed motion, these mechanisms have the potential to be used for lunar takeo simulations. Thus, this paper presents a parallel mechanism driven by nine cables. The purpose of this study is to optimize the dimensions of the cable-driven parallel mechanism to meet dynamic workspace requirements under cable tension constraints. The dynamic workspace requirements are derived from the kinematical function requests of the lunar takeo simulation equipment. Experimental design and response surface methods are adopted for building the surrogate mathematical model linking the optimal variables and the optimization indices. A set of dimensional parameters are determined by analyzing the surrogate mathematical model. The volume of the dynamic workspace increased by 46% after optimization. Besides, a force control method is proposed for calculating output vector and sinusoidal forces. A force control loop is introduced into the traditional position control loop to adjust the cable force precisely, while controlling the cable length. The e ectiveness of the proposed control method is verified through experiments. A 5% vector output accuracy and 12 Hz undulation force output can be realized. This paper proposes a cable-driven parallel mechanism which can be used for lunar takeo simulation.
基金supported by the National Natural Science Foundation of China(No.61304223)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20123218120015)
文摘We first analyzed the force and motion of naval aircraft during launching process.Further,we investigated the ship deck with the form of a ramp and established deck motion model and ship airwake model.Finally,we conducted simulations at medium sea.Results showed that the effects of deck motion on takeoff varied with initial phases,and airwake could help reducing aircraft′s sinkage.We also found that the deck motion played a major role in the effects caused by the interaction of deck motion and ship airwake.
文摘Battery powered vertical takeoff and landing(VTOL) aircraft attracts more and more interests from public, while limited hover endurance hinders many prospective applications. Based on the weight models of battery, motor and electronic speed controller, the power consumption model of propeller and the constant power discharge model of battery, an efficient method to estimate the hover endurance of battery powered VTOL aircraft was presented. In order to understand the mechanism of performance improvement, the impacts of propulsion system parameters on hover endurance were analyzed by simulations, including the motor power density, the battery capacity, specific energy and Peukert coefficient. Ground experiment platform was established and validation experiments were carried out, the results of which showed a well agreement with the simulations. The estimation method and the analysis results could be used for optimization design and hover performance evaluation of battery powered VTOL aircraft.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51505031)
文摘A nonlinear and time-varying gyroplane jump takeoff dynamics model considering the unsteady ground effect and the rapid blade-pitch increase(RBPI) is developed and validated against the experiment data.The precisions of the proposed model,an experienced Hollmann model and three other simplified models are compared by displaying the height and rpm time histories of those models and the experimental data.The mean square errors(MSE) of the height histories and maximum height errors(MHE) between those models are calculated and given out.The statistics provide a kind of evaluation method of importance of the unsteady ground effect,RBPI,and the induced velocity on jump takeoff performance in vertical phase.The impact of the unsteady ground effect and RBPI on the thrust and induced velocity of the experimental rotor of a small scale platform is analyzed.The study indicates that the proposed model agrees better with the experimental data than other models.It is useful for predicting the gyroplane jump takeoff performance for design.
文摘The formal modeling and verification of aircraft takeoff is a challenge because it is a complex safety-critical operation.The task of aircraft takeoff is distributed amongst various computer-based controllers,however,with the growing malicious threats a secure communication between aircraft and controllers becomes highly important.This research serves as a starting point for integration of BB84 quantum protocol with petri nets for secure modeling and verification of takeoff procedure.The integrated model combines the BB84 quantum cryptographic protocol with powerful verification tool support offered by petri nets.To model certain important properties of BB84,a new variant of petri nets coined as Quantum Nets are proposed by defining their mathematical foundations and overall system dynamics,furthermore,some important system properties are also abstractly defined.The proposed QuantumNets are then applied for modeling of aircraft takeoff process by defining three quantum nets:namely aircraft,runway controller and gate controller.For authentication between quantum nets,the use of external places and transitions is demonstrated to describe the encryptiondecryption process of qubits stream.Finally,the developed takeoff quantum network is verified through simulation offered by colored petri-net(CPN)Tools.Moreover,reachability tree(RT)analysis is also performed to have greater confidence in feasibility and correctness of the proposed aircraft takeoff model through the Quantum Nets.
基金supported by National Natural Science Foundation of China(51475028,61703023).
文摘The bio-inspired aerial–aquatic vehicle off ers attractive perspectives for future intelligent robotic systems.Cormorant’s webbed-feet support water-surface takeoff is a typical locomotion pattern of amphibious water birds,but its highly maneuverable and agile kinetic behaviors are inconvenient to measure directly and challenging to calculate convergently.This paper presents a numerical Computational Fluid Dynamic(CFD)technique to simulate and reproduce the cormorant's surface takeoff process by modeling the three-dimensional biomimetic cormorant.Quantitative numerical analysis of the fluid flows and hydrodynamic forces around a cormorant’s webbed feet,body,and wings are conducted,which are consistent with experimental results and theoretical verification.The results show that the webbed feet indeed produced a large majority of the takeoff power during the initial takeoff stage.Prior lift and greater angle of attack are generated to bring the body off the water as soon as possible.With the discussion of the mechanism of the cormorant’s water-surface takeoff and the relevant characteristics of biology,the impetus and attitude adjustment strategies of the aerial–aquatic vehicle in the takeoff process are illustrated.
文摘Since the construction industry has been adopting Building Information Modeling(BIM)as the standard practice for design,engineering,and fabrication in the recent decade,many Construction Management(CM)programs at U.S.universities have started to introduce BIM for cost estimating in their curriculum.Although considered as the fifth dimension beyond 3D and schedule,BIM for cost estimating in many cases is still used merely as an alternative model-based quantity takeoff method to the traditional plan-based approach.The disconnection between automated quantity takeoff and cost estimating,however,still exists,and the benefits of the BIM process in a project life cycle can not be fully understood by CM students without realizing its impact in the preconstruction phase.To bridge these gaps in a CM curriculum,an Advanced Cost Estimating course for CM programs has been developed that focuses on integrating BIM in both the takeoff and estimating process.The new course streamlines the connection between model-based quantity takeoff and cost estimating with the help of a combination of multiple construction software programs.Through the integration between the software,quantity data from a BIM model can be seamlessly transferred to a construction cost database for bid pricing and reporting.This paper presents the development of the new Advanced Cost Estimating course as a case study,including its objectives,layout,and assessment methods,and provides empirical and valuable insights on how to integrate BIM in a cost estimating course for a CM curriculum.
基金supported by the National Natural Science Foundation of China(11232002)the 111 Project(B07009)
文摘In the paper, we present a detailed analysis of the takeoff mechanics of fruitflies which perform voluntary takeoff flights. Wing and body kinematics of the insects during takeoff were measured using high-speed video techniques.Based on the measured data, inertia force acting on the insect was computed and aerodynamic force and moment of the wings were calculated by the method of computational fluid dynamics. Subtracting the aerodynamic force and the weight from the inertia force gave the leg force. The following has been shown. In its voluntary takeoff, a fruitfly jumps during the first wingbeat and becomes airborne at the end of the first wingbeat. When it is in the air, the fly has a relatively large "initial" pitch-up rotational velocity(more than5 000°/s) resulting from the jumping, but in about 5 wingbeats, the pitch-up rotation is stopped and the fly goes into a quasi-hovering flight. The fly mainly uses the force of jumping legs to lift itself into the air(the force from the flapping wings during the jumping is only about 5%–10% of the leg force). The main role played by the flapping wings in the takeoff is to produce a pitch-down moment to nullify the large "initial" pitch-up rotational velocity(otherwise, the fly would have kept pitching-up and quickly fallen down).
文摘Owing to the strong coupling among the hydrodynamic forces,aerodynamic forces and motion of amphibious aircraft during the water takeoff process,the water takeoff performance is difficult to calculate accurately and quickly.Based on an analysis of the dynamics and kinematics characteristics of amphibious aircraft and the hydrodynamic theory of high-speed planing hulls,a suitable mathematical model is established for calculating the hydrodynamics of aircraft during water takeoff.A pilot model is designed to illustrate how pilots are affected by the lack of visual reference and the necessity to simultaneously control the pitch angle,flight velocity and other parameters during water takeoff.Combined with the aerodynamic model,engine thrust model and aircraft motion model,a digital virtual flight simulation model is developed for amphibious aircraft during water takeoff,and a calculation method for the water takeoff performance of amphibious aircraft is proposed based on digital virtual flight.Typical performance indicators,such as the liftoff time and liftoff distance,can be obtained via digital virtual flight calculations.A comparison of the measured flight test data and the calculation results shows that the calculation error is less than 10%,which verifies the correctness and accuracy of the proposed method.This method can be used for the preliminary evaluation of airworthiness compliance of amphibious aircraft design schemes,and the relevant calculation results can also provide a theoretical reference for the formulation of flight test plans for airworthiness certification.
